1. Field of the Invention
This invention relates to a method of driving an image pickup device, and more particularly to a method of driving an image pickup device preferably used in photoelectric transducers (photoelectric conversion devices) formed by a large-area process, as exemplified by two-dimensional photoelectric transducers which perform equal-size reading, such as facsimile machines, digital copying machines and X-ray imaging devices.
2. Related Background Art
Reading systems employing reduction optical systems and CCD type sensors have been used as reading systems such as facsimile machines, digital copying machines and X-ray imaging devices. In recent years, however, development of photoelectric conversion semiconductor materials as typified by hydrogenated amorphous silicon (hereinafter “a-Si”) has brought about remarkable development on what is called contact type sensors, in which photoelectric conversion elements and signal-processing components are formed on a large-area substrate and information is read with an optical system which is equal-size to the information source. In particular, the a-Si has an advantage that it can be used not only as a photoelectric conversion material but also as a semiconductor material for thin-film field-effect transistors (hereinafter “TFT”) and hence a photoelectric conversion semiconductor layer and a TFT semiconductor layer can simultaneously be formed.
However, performance specifications required for large-area photoelectric transducers become severer year by year. Especially in the two-dimensional photoelectric transducers which perform equal-size reading, such as X-ray imaging devices inclusive of those for internal examination or non-destructive examination, it is required to reduce as far as possible the doses of X-rays, which affect human bodies, and to obtain more highly precise data uniformly and in a short time in the two-dimensional area. Under such requirements, it is required to make as small as possible any uneven signal outputs from photoelectric conversion elements and to drive the devices in a short time.